后缀表达式转化为前缀表达式并求值

#include

#include

#include

#define STACK_INIT_SIZE 100

#define STACKINCREMENT 10

#define OK 1

#define OVERFLOW -2

#define ERROR 0

#define TRUE 1

#define FALSE 0

typedef int Selemtype;

typedef int Status;

#define MAX 50

char string1[MAX]; //定义两个字符串分别存放中缀表达式和后缀表达式char string2[MAX];

int result;

typedef struct

{

Selemtype *base; //在构造之前和销毁之后，base的值为NULL

Selemtype *top; //栈顶指针

int stacksize; //当前分配的存储空间，以元素为单位

}SqStack;

Status InitStack(SqStack *S);

Status Push(SqStack *S,Selemtype e);

Status Pop(SqStack *S,Selemtype e);

Status InitStack(SqStack *S)

{ //构造一个空栈S

S->base=(Selemtype*)malloc(STACK_INIT_SIZE*sizeof(Selemtype));

if(!S->base) return OVERFLOW; //存储分配失败

S->top=S->base;

S->stacksize=STACK_INIT_SIZE;

return OK;

}

Status Push(SqStack *S,Selemtype e)

{ //插入元素e为新的栈顶元素

if(S->top-S->base>=S->stacksize)

{ //栈满，追加存储空间

S->base=(Selemtype*)realloc(S->base,(S->stacksize+STACKINCREMENT)*sizeof(Selemtype));

if(!S->base) return OVERFLOW; //存储分配失败

S->top=S->base+S->stacksize;

S->stacksize+=STACKINCREMENT;

}

*S->top++=e;

return OK;

}

Status Pop(SqStack *S,Selemtype e)

{ //若栈不空值，则删除S的栈顶元素，用e返回其值，并返回OK,否则返回ERROR

if(S->top==S->base) return ERROR;

e=*--S->top;

return OK;

}

Status StackEmpty(SqStack *S)

{ //若栈S为空，则返回TRUE,否则返回FALSE

if(S->top==S->base)

return TRUE;

else

return FALSE;

}

Selemtype GetTop(SqStack *S)

{ //取栈顶元素并用e返回其值

Selemtype e;

if(S->top==S->base) return ERROR;

e=*(S->top-1);

return e;

}

void transform(char str1[],char str2[])

{ //将中缀表达式转换为后缀表达式

SqStack Op;

InitStack(&Op); //定义一个空栈用来存放运算符

Push(&Op,'#');

Selemtype top; //取得运算符栈的栈顶元素赋值给top

Selemtype e=NULL; //出栈的栈顶元素赋值给e

int i=0,j=0,m;

char a;

m=strlen(str1);

for(i=0;i

{

a=str1[i];

if('0'<=str1[i]&&str1[i]<='9') //如果是操作数直接放在后缀表达式中

{

str2[j]=str1[i];j++;

}

else

{

str2[j]=' ';

j++;

switch(a)

{

case '(':{

Push(&Op,a);

} break;

case '*':

case '/':

top=GetTop(&Op);

if((top=='*')||(top=='/'))

{

Pop(&Op,e);

str2[j]=top;j++; //比其高，现将栈顶运算符出栈，再进栈。

Push(&Op,a);

}

else

{

Push(&Op,a);

} break;

case '+':

case '-':

top=GetTop(&Op);

if(top=='+'||top=='-'||top=='*'||top=='/')

{

Pop(&Op,e);

str2[j]=top;j++;

Push(&Op,a);

}

else

{

Push(&Op,a);

} break;

case ')':{

top=GetTop(&Op);

Pop(&Op,e);

while(top!='(')

{

str2[j]=top;

j++;

top=GetTop(&Op);

Pop(&Op,e);

}

} break;

}

}

}

top=GetTop(&Op);

Pop(&Op,e);

while(top!='#')

{

str2[j]=top;

j++;

top=GetTop(&Op);

Pop(&Op,e);

}

str2[j]=top;

printf("转化后的后缀表达式为:%s\n",str2);

}

Selemtype counttem(char str[])

{ //计算后缀表达式的值

SqStack S;

InitStack(&S);

int len;

len=strlen(str);

Selemtype A[10];

int m,n,p,e=NULL,k,E;

int i,j,l,ch,zh; //zh为字符型转化为的整形数

for(i=0;i

{

if('0'

{

k=i;j=0;

while('0'<=str[k]&&str[k]<='9') //将字符型的一串数字转化为整形

{

A[j]=str[k]-48;

j++;

k++;

}

ch=A[j-1];

E=1;

for(l=1;l

{

E=10*E;

zh=A[j-l-1]*E;

ch+=zh;

}

Push(&S,ch);

i=k-1;

}

else if(str[i]=='+'||str[i]=='-'||str[i]=='*'||str[i]=='/')

{

m=GetTop(&S);

Pop(&S,e);

n=GetTop(&S);

Pop(&S,e);

switch (str[i])

{

case'+':

p=m+n; break;

case'-':

p=n-m; break;

case'*':

p=n*m; break;

case'/':

p=n/m; break;

}

Push(&S,p);

}

else if(str[i]==' ')

{

}

else if(str[i]=='#')

{

result=GetTop(&S);

}

}

printf("表达式的运算结果为：%d\n",result);

return result;

}

void main()

{

printf("请输入表达式（整数的四则运算）");

gets(string1); //用字符串string1盛放中缀表达式

transform(string1,string2); //用字符串string2盛放后缀表达式counttem(string2);

}